Error type: "Bad Request". Error message: "API key not valid. Please pass a valid API key." Domain: "global". Reason: "badRequest". 
Did you added your own Google API key? Look at the 
help.
Check in YouTube if the id 
PLixfoKbEpkFtv5ygsaLFWEpZlZPwEfBpz belongs to a playlist. Check the 
FAQ of the plugin or send error messages to 
support.